[vfio-users] Interrupt Handling: Regression or config change?

[Ede Wolf]

Hello,

Running arch, I am having a windows XP guest, to which I am passing 
through a PCIe Parallel Card, that again talks to a device that 
unfortunately is very picky about interrupts and more so the interrupt 
setting within Windows XP for that parallel port.

For a short explanation: Windows XP offers 3 ways to operate the 
parallel port:
"never use an interrupt"
"try not to use an interrupt"
"Use any interrupt assigned to that port"

My device requires the last option, otherwise communication does simply 
not work, albeit the device itself is detected. So it seems, that 
whatever setting I choose within windows xp, it is now ignored and does 
not make any difference any more.

However, it used to work perfectly fine up to Kernel 4.5. or 4.6, I do 
not remember exactly, but does not work any more with 4.8. Skipped 4.7 
for sure.

Booting into the 4.4-lts kernel makes things work as expected, booting 
into 4.8.x and communication is broken again. Can be repeated at will 
with consistently the same results and holds true now for several 
incarnations of the 4.8 kernel the archlinux team has provided so far.

Now I am wondering: Is there any compelling configuration change that I 
am not aware of or is this simply a bug? And if, is this related to vfio 
or other parts of the kernel and this the wrong place?

Thanks for any help


Ede